Page 68 - E-Modul Termokimia Berbasis PBL

(CH 2) 3(g) + O 2(g) → 3CO 2(g) + 3H 2O (l) ∆H reaksi = -2091,4 kJ mol
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Jika diketahui ∆H f CO 2(g) = -393,5 kJ mol dan ∆H f H 2O (l) = -285,8 kJ
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mol , hitunglah entalpi pembentukan standar siklopropana!
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Diketahui:
Reaksi pembakaran siklopropana:

(CH 2) 3(g) + O 2(g) → 3CO 2(g) + 3H 2O (l) ∆H reaksi = -2091,4 kJ mol
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∆H f CO 2(g) = -393,5 kJ mol
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∆H f H 2O (l) = -285,8 kJ mol -1
Ditanya:
Entalpi pembentukan standar siklopropana (∆H f (CH 2) 3) !
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Jawab:

∆H reaksi = ∑∆H f produk - ∑∆H f reaktan
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-2091,4 kJ mol = [(3x∆H f CO2) + (3x∆H f H2O(l))] – [(∆H f (CH2)3) + ( x ∆H f O2)]
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-2091,4 kJ mol = [(3x(-393,5) kJ mol ) + (3x(-285,8 kJ) mol )] - [(∆H f (CH2)3) + ( x 0)]
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-2091,4 kJ mol = [(-1180,5) kJ mol + (-857,4) kJ mol ] – [(∆H f (CH2)3) + (0)]
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-2091,4 kJ mol = [(-2037,9) kJ mol - [(∆H f (CH2)3)]
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(∆H f (CH2)3) = [(-2037,9) + 2091,4 kJ mol ]
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(∆H f (CH2)3) = +53,5 kJ mol
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Jadi, entalpi pembentukan standar siklopropana sebesar +53,5 kJ
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mol .

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